1. Field of the Invention
The present invention relates to an ophthalmic apparatus, and more particularly to an alignment mechanism of the ophthalmic apparatus for aligning an operation apparatus and a measuring apparatus with a patient's eye.
2. Description of Related Art
FIG. 1 shows a typical alignment mechanism used in a known ophthalmic operation apparatus and a known measuring apparatus.
In the alignment mechanism, which provides a light source 2 arranged at the oblique above position of an examinee's eye 1, lenses 3, 4 and a light detector 5, a light beam emitted from the light source 2 is condensed through the lens 3 on an apex of cornea of the examinee's eye 1, and reflected thereon. The reflected light is again focused through the lens 4 toward the light detector 5 arranged at a focus position of the lens 4, and detected thereby.
This alignment method, although being able to obtain satisfactory alignment precision thereby, has only a very limited detectable scope. Accordingly, the alignment light may be focused out of the light detector 5 if the position (of the apparatus) is even slightly dislocated.
In addition to the above problem, this alignment method needs a display means to display a detected result by the light detector 5 on an observing system including a microscope or a TV monitor or the like, whereby the alignment mechanism may become complicated.
Another alignment mechanism shown in FIG. 2 has also been proposed. In the alignment mechanism, lasers 6a and 6b are arranged respectively at right and left oblique above positions of an examinee's eye 1. The respective laser beams emitted from the two lasers 6a and 6b irradiate the examinee's eye 1 and form laser spots thereon, the laser spots are then observed through an observing system 7 arranged on the optical axis of the examinee's eye 1. Thus, the alignment is adjusted so as to correspond the laser spots each other on the examinee's eye 1, namely, the focus position (alignment) is correct when laser spots by the two lasers 6a and 6b become one laser spot 8 as shown in FIG. 3(a), the examinee's eye 1 is too near than a proper focus position when two laser spots 8a and 8b are separate spots as shown in FIG. 3(b), and the examinee's eye 1 is too far than a proper focus position when two laser spots 8a and 8b are changed places with each other as shown in FIG. 3(c).
The alignment method needs corresponding two small laser spots formed on the examinee's eye, however, the reflected plane on which the light beams are reflected toward the observing system is the curved cornea surface of the examinee's eye. Accordingly the small spots are even difficult to observe. And further, when the examinee's eye 1 is positioned either too near (b) or far (c) than a proper focus position, the operator may observe the two spots in a same view, thereby can not judge whether a distance between the examinee's eye and the apparatus is too short or long to determine an alignment direction to which the apparatus should be moved.